It's called biochar, and if you believe its most ardent supporters, then this unassuming, fine black powder is a vital tool in the solutions to some of humanity's most urgent ecological threats, including climate change, peak oil, soil degradation and water pollution due to agrochemicals. However, if you side with biochar's staunch opponents, then it seems like a fledgling, poorly understood technology with real risks, including the displacement of entire communities and the serious jeopardizing of world food security and biodiversity. Which view is correct? That's the question that sustainability expert James Bruges, who is cautiously optimistic about biochar, investigates in his book The Biochar Debate.

Biochar is essentially charcoal made through a process called pyrolysis (which involves burning organic material in the absence of oxygen), and then finely crushed and worked into the earth as a soil amendment.* The pyrolysis process has two byproducts, syngas and bio-oil, which can be used for generating heat and power, hence biochar's appeal to alternative energy enthusiasts. And once the biochar is in the soil, it has an amazing ability to retain nutrients and moisture due to its unbelievably porous structure (a single gram can have twice the surface area of a tennis court). This enables it to dramatically boost crop yields and reduces the need for industrial fertilizers. Thus, biochar has the potential to simultaneously ensure our future food supply and wean croplands off of the poisons in which they must be doused in order for today's mineral-depleted soils to sustain production. Another advantage of biochar is that it can be made from virtually any organic material (from manure to wood to switchgrass), meaning that there would be no shortage of suitable feedstocks, and biochar production could double as a waste recycling scheme.

Most important of all, however—assuming that climate scientists have called it correctly with their warnings of an imminent, irreversible climate tipping point—is biochar's ability to pull substantial quantities of CO2 and other greenhouse gases from the atmosphere and trap them underground effectively forever, in human terms. Biochar's oft-repeated sales pitch is that it isn't merely carbon-neutral, it's "carbon-negative." And this capacity for sequestering carbon could, conceivably, allow us to return atmospheric CO2 to pre-industrial levels within our lifetimes.

The technology certainly has backing from serious heavyweights in the environmental community. One of these backers, Bill McKibben, founded the 350 campaign, which advocates reducing atmospheric CO2 from its current concentration of nearly 390 parts per million (ppm) to its safe upper limit of 350 ppm. Also strongly in favor of biochar is James Lovelock, originator of the Gaia theory (which says that the Earth is one complex, self-regulating system—a single organism, if you like). Moreover, some of the main beneficial properties of biochar have been documented in a growing body of scientific literature. But biochar has also raised deep concern among many environmentalists and environmental groups. These groups include the Climate Outreach and Information Network (U.K.), Biofuelwatch (U.K.), the Organic Consumers Association (U.S.), the Rainforest Action Network (U.S.) and, ironically, even the Gaia Foundation (U.K.)—the namesake of biochar-supporter Lovelock's aforementioned theory—among nearly 150 other organizations in several dozen countries. These organizations have questioned many of the claims that have been made about biochar's potential (including, most damningly, its very carbon sequestration benefit), and have branded it as "a new big threat to people, land, and ecosystems."**

Bruges freely acknowledges the need for much additional research into the workings of biochar—as well as more conclusive proof of all the claims made on its behalf. He also acknowledges biochar’s potential risks, though he claims that they're acceptable considering the urgent need to reduce atmospheric CO2 levels. And he makes a compelling case that this could be done using biochar. He takes heart from the following two calculations by Craig Sams, a former chairman of the U.K.'s Soil Association: first, that devoting all of the world's productive land to biochar production would return atmospheric CO2 to pre-industrial levels (280 ppm) within just a year; and, second, that giving a mere 2.5 percent of the world's productive land over to biochar production would bring CO2 to pre-industrial levels by 2050. The first of these scenarios obviously isn't a viable option, since it would leave us no land for growing our food. However, Bruges shows that the second scenario is easily doable, in light of a recent report by the Food and Agriculture Organization of the United Nations (FAO) and the Organisation for Economic Co-operation and Development (OECD) showing that an additional 4 billion acres could be added to the world's existing 3.5 billion acres of cropland.

Clearly geared toward a lay readership, The Biochar Debate begins by succinctly summing up climate change, peak oil, peak phosphorus and other important issues related to the Earth's ecological limits. Then it gets into somewhat less familiar territory: biochar and its fascinating history. It is only within the past decade that biochar has really begun to show up on the radar screen, but its roots are ancient, going all the way back to fifth century B.C. South America. There, in the deep jungles of the Amazon Basin, one of the great, thriving agrarian societies in our planet's history devised a sustainable agriculture involving the use of human-made charcoal to enrich the Basin's naturally thin, infertile soils.

Today, locals refer to this ancient soil as terra preta, or "black earth." We know that it's human-made because it contains shards of ancient pottery, indicating a great deal of human handling during its formation. And even now, five centuries after the disappearance of that great Amazonian civilization, terra preta continues to retain its amazing fertility and carbon content, and in fact is commercially harvested and sold to local farmers. This has promising implications for modern-day biochar, which, once added to the soil, should continue to improve fertility and retain its sequestered carbon for hundreds or even thousands of years to come. (Lacking the original recipe, however, soil ecologists have thus far been unable to precisely replicate terra preta—and critics often point this out when calling biochar's viability into question.)

Again, Bruges readily acknowledges biochar's potential risks, in spite of how strongly he feels in favor of it. The main risks that he foresees have to do with letting market forces, rather than government oversight, regulate biochar's production. Bruges believes that if regulation is left to the market, then companies may try to capitalize on the fuels that come as byproducts of biochar, rather than on the biochar itself, if these byproducts prove more profitable (with obvious implications for the climate). He also fears that crops for making biochar and its associated fuels could begin to supplant food crops, if corporate profits dictate this action. (This worry seems frighteningly valid in light of the soaring food prices that went hand-in-hand with the height of the ethanol craze.) Further, Bruges warns that if policies are enacted that allow farmers to earn carbon credits for their biochar, then big agriculture, in its haste to cash in on the bonanza, may set up large-scale, environmentally destructive monocultures of grass and fast-growing trees to be used as biochar feedstocks.

In addition to orienting lay readers with regard to climate change, peak oil and other important background facts, describing biochar's science and fascinating history, weighing its merits against its potential pitfalls and presenting a compelling case for its immediate, large-scale use, The BiocharDebate discusses at length the various pilot schemes that have been conducted with biochar to date. Some of these pilot schemes are inspiring success stories, while others serve as instructive examples of things that can go wrong. To take one example on the success story side, Bruges describes a banana plantation in India where, following the introduction of biochar, yields per tree have risen by 44 percent, the bananas keep longer and apparently taste better, the farmer is able to get a better price for them than before and the amount of time spent each day irrigating has been cut in half. And as an example of what not to do, Bruges takes us to a tiny village in Ghana where biochar is having a hard time taking off because the farmers lack secure rights to the land that they cultivate. Most of the farmers don't own their farmland—instead they rent it, and then only for a year or two at a time—and thus they have little incentive to invest in the soil.

All in all, The Biochar Debate is a spirited yet critical look at a controversial emerging technology that could potentially go a long way toward mitigating climate change, restoring depleted soils and maintaining our food security into the future. Besides being extremely knowledgeable about biochar, Bruges is also quite opinionated about it and has many thoughts on how its subsidization, oversight, certification and research and development might best be handled. And he backs up all of these opinions and recommendations with solid evidence and real-world examples from his many travels to places around the world where biochar is being used successfully. The book also does a good job of pointing readers toward resources for further reading, as well as describing small ways in which each of us can be contributing something to the cause. And Bruges' conviction that successfully heading off a climate catastrophe is worth taking some calculated risks with biochar—or with any number of other climate change mitigation technologies that may yet emerge—is certainly well-taken.